1. Field of the Invention
The present invention relates to a process for wastewater treatment in order to remove nitrogen and phosphorus as well as organic substances in wastewater. More particularly, the present invention relates to a process for wastewater treatment using an Intermittently Decanted Extended Aeration (IDEA) procedure comprising a cycle procedure wherein three periods of aeration, settling and decanting are successively repeated in that order in a single reactor.
2. Description of the Prior Art
In the past, wastewater treatment plants usually aimed at the removal of organic substances and suspended solids in wastewater. Accordingly, in conventional wastewater treatment, many inorganic nutrients such as nitrogen and phosphorus were not removed and discharged into lakes and marshes. This resulted in eutrophication of lakes and marshes, which makes it difficult to provide clean water resources and preserve the ecological system. For example, in wastewater treatment plants, the removal rate of organic substances is 80% or more, but nitrogen and phosphorus are not efficiently removed and discharged together with wastewater. Such wastewater containing nitrogen and phosphorus which is discharged into lakes and marshes induces excessive proliferation of algae, which makes it difficult to provide high-quality water resources. As a result, the costs for wastewater treatment are dramatically increased and an advanced treatment for purifying wastewater is further required.
Accordingly, several processes for removal of various nutrients present in wastewater are proposed in the art. They may be roughly categorized into a process for removal of nitrogen, a process for removal of phosphorus and a process for simultaneous removal of nitrogen and phosphorus.
A conventional process for wastewater treatment uses a cycle process of nitrification and denitrification by microorganism for removal of nitrogen, and the principle of anaerobic-aerobic process which is carried out through aerobic luxury uptake of phosphorus released under anaerobic and anoxic condition by microorganism for removal of phosphorus.
For example, there are Bardenpo""s process being referred as a process for simultaneous removal of nitrogen and phosphorus, and anaerobic-aerobic process (A/O process) and A2/O process being referred as a process for biological removal of phosphorus. Additionally, there is a process for the treatment of wastewater such as a chemical precipitation which uses a general coagulant such as aluminum and lime, and ammonia-stripping process.
However, each of the conventional processes as mentioned above has defects in accordance with its operative characteristics. Such defects are summarized in Table 1.
As a result of an extensive investigation in order to eliminate defects of conventional processes described in the above Table 1, and to develop the process for removal of nitrogen and phosphorus as well as organic substances with high degree of efficiency, the present inventors accomplished the present invention.
It is therefore an object of the present invention to provide a process for wastewater treatment using an Intermittently Decanted Extended Aeration (IDEA) procedure characterized in that three periods of aeration, settling and decanting are successively repeated in that order in a single reactor, wherein the influent wastewater is transversely supplied in bottom of the reactor and slowly diffused in the reactor for the entire period of the procedure while the treated wastewater is intermittently discharged only during decanting period.
It is another object of the present invention to provide a process for wastewater treatment using the IDEA procedure wherein three periods of aeration, settling and decanting are successively repeated in that order in a single reactor, characterized in that said aeration period comprises a first phase which is carried out by small amounts of oxygen with feeding outside carbon source and a second phase which is carried out by large amounts of oxygen according to the control of the amount of oxygen to be fed in the aeration period.
Further objects and advantages of the invention will become apparent through reading the remainder of the specification.